Activity standardization of 22Na

The activity of a 22Na solution was measured by means of two 4πβ−γ coincidence-counting techniques. The first method corresponds to the classical 4πβ−γ coincidence counting and requires the β+-branching ratio. The second procedure is based on a variation of the distance between source and gamma detector. The efficiency for detecting the sum peak is then extrapolated to zero, giving the total source activity. The combination of both methods yields the β+ branching ratio. In addition, liquid scintillation counting using the CIEMAT/NIST-method as well as a secondary standardization by means of calibrated ionization chambers were used for activity determination. The results were checked for consistency and an ampoule was submitted to the BIPM to have the activity result entered into the database of the International Reference System (SIR).